1. Field of the Invention
The present invention relates to optical networks and, more specifically, to restoration planning in packet-over-optical networks.
2. Description of the Related Art
A popular architecture for telecommunications networks is known as packet-over-optical. This architecture employs an optical transport layer, for example, a Synchronous Optical Network (SONET)) or frame relay layer, overlaid with a packet layer, for example, Internet protocol (IP), IP over multiprotocol label switched (MPLS), asynchronous transfer mode (ATM) or frame relay. With the deployment of high-capacity, for example, gigabit-per-second range, transmission and switching equipment within these networks, any single-link outage or single-node outage can lead to tremendous losses for both the network operators and their customers. As a result, it has become important to design these networks in such a way that they can quickly recover from network failure and restore interrupted traffic.
There are many different types of network failures, but, in a packet-over-optical network, two types of failures predominate. These are (1) failures in the optical transport layer including optical cross-connect (OXC) failures, transmitter failures, or fiber/cable cuts, and (2) failures in the packet layer including different failure modes of packet-layer routers. The failure modes of packet-layer routers include misconfiguration, processor or line-card failure, power glitches, or power-supply failure. Generally, in packet-over-optical networks, transport-layer optical cross-connect failures are much less likely than router-related failures. Indeed, anecdotal evidence from network operators suggests that router failures are responsible for up to forty percent of outages in today's packet-over-optical networks. This is because rapidly growing packet networks are faced with constant software and hardware upgrades, and routers are generally not as reliable as traditional telecommunication equipment. Typically, the optical transport layer includes mechanisms to recover from transport-layer failures, while the packet layer includes mechanisms to recover from packet-layer failures. These mechanisms include the reservation of restoration capacity for each layer.